Quick answer: Who’s is a contraction of who is or who has — the apostrophe stands in for the missing letters. Whose is the possessive form of who, meaning “belonging to whom.” If you can swap in “who is” or “who has” and the sentence still makes sense, write who’s; if you can’t, you need whose.
These two words are homophones — they sound exactly the same — which is why they get muddled so often. In writing, though, they do completely different jobs, and picking the wrong one is a small error that readers notice instantly. Autocorrect and spellcheck will not save you here, because both spellings are real words.
Here is the trap that catches almost everyone. With ordinary nouns, an apostrophe plus s normally signals possession — Sarah’s coat, the dog’s lead — so instinct says the possessive word should be the one with the apostrophe. With pronouns, that instinct is exactly backwards. Possessive pronouns never use an apostrophe: its, hers, ours, theirs, yours — and whose. The apostrophe in who’s is doing one job only: marking a contraction. Once you internalise that, the confusion largely disappears.
Use who’s only when you genuinely mean who is or who has. The test is simple: expand it in your head. If the full form works, the apostrophe is right.
Who’s = who is:
Who’s = who has:
Use whose when you are talking about possession or belonging — whether you are asking a question or linking two parts of a sentence together.
Seeing the two side by side is the fastest way to fix the habit:
Most people lock onto who is and forget the other half. Who’s is also short for who has, especially before a past participle such as been, done, seen or got. So Who’s been eating my porridge? unpacks to who has been, and takes the apostrophe. If you can slot in who has, who’s is correct.
A stubborn myth insists that whose may only describe people. It is not true. English has no possessive form of which, so whose has done duty for objects, animals and abstract ideas for centuries: a house whose windows were broken, a theory whose implications are troubling. The supposedly “correct” alternative, of which, is grammatical but usually clumsy — a house the windows of which were broken. Use whose without hesitation.
Both words appear in relative clauses — the part of a sentence that adds information about a noun — and that is where the slip is easiest. Compare the man whose car broke down (the car belongs to him) with the man who’s just arrived (the man who has just arrived). Read the clause on its own and the right choice is usually obvious.
Two quick oddities. The phrase a who’s who (a list of notable people) uses the contraction — it literally means who is who: The gala was a who’s who of British theatre. And the possessive of who else is who else’s, not whose else: Who else’s idea could it possibly be?
No. This is one of the rare points where the two main varieties of English agree completely. The spelling, the meaning and the usage of who’s and whose are identical in American, British, Australian, Canadian and every other standard form of English. There is no regional wrinkle to memorise here — the rule you have just read applies everywhere.
Keep two quick checks in your back pocket:
Who's is a contraction of who is or who has, where the apostrophe replaces missing letters — Who's calling? Whose is the possessive form of who, showing ownership — Whose phone is that? A quick test: if you can expand the word to who is or who has, use who's; otherwise use whose.
It's whose birthday. Whose shows possession — the birthday belongs to someone — so Whose birthday is it? is correct. Who's would mean who is birthday, which makes no sense. The same logic applies to whose turn, whose fault and whose idea: all are possessive, so none takes an apostrophe.
Whose fault. You're asking who a fault belongs to, so you need the possessive whose — Whose fault was it? Write who's fault only if you genuinely mean who is fault, which never happens. Fault, like turn and job, is a thing being owned, so the possessive whose is always right here.
Yes. Although whose comes from who, standard English uses it for animals, objects and abstract ideas too, because there's no possessive form of which. So a car whose engine failed and a plan whose flaws were obvious are both correct. The alternative, of which, is grammatical but usually sounds stiff and old-fashioned.
Who's ready. Here who's means who is — Who is ready to go? — so it takes an apostrophe. Whose ready would wrongly suggest ready is a possession. Whenever a describing word or verb follows, like ready, coming or going, you almost always want who's (who is), not the possessive whose.
